Apparatus for pulverizing material



Dec. 3, 1929.

w. J. A. LONDON 1,737,800 APPARATUS FOR PULVERIZING MATERIAL il y 1928 2 Sheets-Sheet 1 Wflliam klklorldon.

INVENTOR- TTORNEYS Dec. 3, 1929.

W. J. A. LONDON APPARATUS FOR PULVERIZING MATERIAL Filed May 9, 1928 2 Sheets-Sheet 2 h 55 as 29 7 L as Fyca 2 5 47 v fi LU LL 1 wuu'm .J LMO.

IN VEN TOR.

Patented Dec. 3, 1929 V UNITED STATES PATENT OFFICE J. A. LONDON, OF HARTFORD, CONNECTICUT, ASSIGNOB TO PEABODY EN- GINEERING CORPORATION, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK AZPPABATUS FOB PULVERIZING MATERIAL Application filed Kay 9, 1928. Serial No. 276,459.

My invention relates to a method. of and apparatus for reducing materials to a powdered condition and more particularly for producing powdered coal for power plants.

Two methods'of reducing a material to a desired mesh fineness are known, namely, by impact and by attrition. The former is effected by the impact of rotating hammers against the material; the latter by a crushing or grinding action produced by. rollers 'or balls. Both methods have been employed to reduce materials to an ultimate or desired mesh fineness but at the expense of relatively great power consumption per ton of material pulverized.

In the operation of impact mills it has been found that the hammer efieet will reduce the material to a certain average degree of fineness with a relatively small utilization of power. The material after such treatment consists of a mass containing fine particles of dust which requires no furthertreatment, and a considerable percentage of larger particles which, in the majority of cases, are not commercially usable. To reduce these coarser particles to the desired fineness requires a fgreat deal of additional power. One reason for this is that'the particles become too fine to be affected by impact action and must therefore be kept in circulation in the mill for a sufiicient eriod of time to reduce them to the desire fineness by attrition. By reason of the high rotative speeds employed in impact mills and the subsequent windage losses, grinding by attrition in an impact mill is less efiicient than it is in a regular attrition mill without high windage and rotation losses.

One object of my invention is to increase the capacity of an impact mill by discharging the material therefrom after it has been reduced to a fineness short of that desired but containing usable fines, separating the latter and conveying them to the point of utilization or to a storage bin, leaving the coarser particles only to be treated in a mill operating on the attrition principle where the grmding is completed more efliciently than it canbe done in the original impact As the attri 'on mill used by me for the any given mill of the attrition type in tons per hour is also materially increased, and the power consumption per ton materially reduced; Y

My invention will be understood by reference -to the accompanying drawings in I which,

Figure 1 is a view in elevation, certain parts being broken away, of one arrangement which may be employed.

. Figures 2 and 3 are similar views illustrat-- other arrangements of the two mills;

ing These several views are more or less diagrammatic but are suflicient to explain the method employed.

Referring first to Figure 1, A designates a mill of the impact type. B a separator for separating usable fines from unground material, and C an attrition mill for treating the unground material. delivered to it from the separator B. Assuming that coal is the material to be treated, I start with it in the condition in which it is delivered from the mine,

' that is, with its moisture content and without previous drying, although this is not essential. The coal is delivered from. hopper 1 to any suitable type of feeder 2 through a chute 2' to the impact mill A, which may be'of any well known or suitable type. As here shown, this mill comprises a disc 3 carrying hammers 4. The disc is mounted on shaft 5 driven by a motor 6 or other suitable means. As is well known, the rotative speed of the mill is such that the material will be reduced in size by the impact of the hammers. On the shaft 5 is also mounted a disc 7 carrying fan blades 8. A separate fan element consisting of a number of blades 9, which may also be mounted on the disc 7, is located in the hammer chamber for agitating the ground material and assisting in its delivery to-the a1r current created by the fan blades 8. Air is admitted 1 through the open side 10 of the fan casing.

The area/above the fan is divided by a I partition 11 to provide two outlets 12 and 13.

To the farmer is connected a ipe 14 dis charging into the separator B o the cyclone or other efiective .type. That shown comprlses a series of adjustable vanes 15 by which both the velocity and direction of the powdered coal are changed. In the area below the vanes 15 is a hopper 16 havin a discharge pipe 17, leading to the attritlon mill C. pipe 18 fitted to the top of the separator dehvers the powdered coal to a storage bin, or as may be desired.

From the outlet 13' of the impact mill, a pipe 19 leads to the attrition mill for conveymg air thereto from the fan 8. Theshaft 5 is connected to a reducing car 20 which in turn drives the attrition mi at any desired speed. The latter may beof the type comprising a-rotating table and rollers revolving on and in contact with the table. The current .of air entering through pipe 19 sweeps over mill, for regrindmg.

The operation of the system above .de-

scribed is as follows: Assume that coal is to be reduced to a fineness of 200 mesh. As the coal is delivered to the impact mill it will be reduced in size by'the impact of the rotating hammers to a certain degree of fineness which, however, will not be uniform but will vary, for example, from 100 to .200 mesh. The coal is fed to the impact mill in .a practically continuous stream and as the reduced masses are raised by the blades 9, they will be swept upward by the current of air, induced by the fan 8, and carried through-passage 12 and pipe 14 to the separator B. Here the coal passes through the blades 15 and a separation takes place due to the action of centrifugal force. The particles of the desired fineness from the center of the'mass are carried by the air current to the point of consumption or to a storage bll'l as may be desired. The coarser particles drop by gravity into the hopper 16 and are delivered y i 17 to the attrition mill C. In this tli e coarser particles, or those less than -200 mesh fineness, will be reduced by the crushing or grinding action produced by rolls or balls. After being acted upon the masses are swept upward by the air' current delivered through pipe 19, through the space between the separator casing and hopper16 to the separator where they mingle with the particles delivere'd'through pipe 14 and are mill byreducing the time 1,7aaeoo again subjected to the action of centrifu I force to effect a separation between t e particles of the desired fineness and those which are not usable.

From the fore oing description it will be seen that in speafiing of an im act mill I do not exclude. the possibility 0 some of the .material being reduced to the desired fine impact forces or by attrition ined. Also, :in'speaking ofan ness either b or. both, com attrition mill I do not exclude the possibility I that some of the coarser particles may bereduced by forces other than attrition. What I do consider of importance is that I am enabled to increase the capacity of the impact that a given mass of material is subjected to theimpact forces and of imposing upon such mill the duty only of effecting a particle reduction in size of the coal particles, although, as matter of fact,- because of the nature of the operation, a fair percentage will be reduced to the desired fine? ness. This, of course, means increased efiiciency as the mill can be operated with a comparatively low power consumption andit is not required to run it at a rate which would be necessary if called upon to reduce all of the coal to the ultimate desired fineness.

- Similarl with reference to the attrition I that the time required to treat a given mass of material is reduced, and also because the size of the particles treated require less power -mill. In t at case the power consum ion is also materially reduced by reason of t e fact than would be necessary to reducethe initial 10 particles, or those of the size treated in the impact mill. V

It has been found in practice that mills of the impact type can eflectively pulverize coal having a moisture content as high as 15% t9:

20%. Attrition mills cannot so 'efiectively handle wet coal so that it is the general-practice to install driers to extract a large percentage. of the moisture before feeding the material to the mills. In the operation of animpact mill a certain percentage of moisture is dissipated in passing through the mill, By the arrangement shownI am enabled not only to improve the efiiciency of the grinding but can'eflectively handle very wet coal wi out the necessity of introducing expensive driers, as the initial moisture contained issufiicienh ly reduced in passing through the "impact stage to make it workable in the attrition stage.

In Figure,- 2, I show an alternative arr emo ment in which the material to be trim is supplied from the hopper to an impact mill 26. All of the material treated in the impact mill is delivered throughpipe 27 'to'the'sepmill, together-with the air in circulation there- I in, is withdrawn by the fan 32 and delivered through pipe 33 to a separator 34 in which the air is separated from the fines, and permitted to return through pipe 35 to the attrition mill. The fines deposited in separator 34 are discharged through pipe 36 where they meet with the fines going through pipe 29, and are conveyed away through pipe 37. A booster 38 may be introduced into the pipe 37, if desired. Another alternative arrangement is shown in Figure 3 in which I use a type of mill known as a ball and tube mill, in conjunction with an impact mill. In this arrangement the material is fed from the hopper 39 to an impact mill 40 from which it is conveyed by the air current through pipe 41 to a separator 42. The fines from the latter pass through pipe 43 to pipe line 44. The unground particles from the separator 42 are delivered through pipe 45 to the ball and tube mill 46. The necessary circulation of air through this mill is created by the fan 46, the direction of the air currents being shown by the arrows. The material from the ball and tube mill is delivered through pipe 47 to separator 48. The air from the latter is returned to-mill 46 through pipe 50, while the material deposited in separator 48 will be discharged through pipe 49 to line 44. I have here shown the mills driven through a pulley 51, driving the impact mill direct and the ball and tube mill through a reducing gear 52 and train of gears 53.

The mode of operating the systemsillustrated in Figures 2, and 3 will be apparent. The same advantages described in connection with the system illustrated in Fig. 1 are attained in the modified arrangements. In all of the systems illustrated, the impact mill is relieved of the work of reducing all of the material to the desired ultimate fineness, the attrition mill being called upon only to further. reduce the size of the particles which are not reduced in the impact mill to the desired mesh fineness.

What I claim is:

1. A system for pulverizing material comprising two independently operated mills, a separator located between and connected to said mills, said separator having means to separate the usable fines from the product of the first mill and to discharge the unground material into the second mill, and means for returning the ground product of the second mill to the separator.

2. A system for pulverizing material comprising two independently operated mills, a separator located between and connected to said mills, said separator having means to separate the usable fines from the product of the first mill and to discharge by gravity the unground material into the second mill, and means for returning the ground product of the second mill to the separator.

3. A system for pulverizing material comprising two independently operated mills, one of said mills being of the impact type and the other of the attrition type, a separator located between and connected to both of said mills, said separator having means to separate the usable fines from the product of the impact mill and to discharge the unground material into the attrition mill, and means for returning the ground product of the attrition mill to the separator.

4. A system for pulverizing material comprising a grinding mill, a separator, means for conveying all of the material from said mill to the separator, means in the latter for separating the particlesof a desired fineness, a second grinding mill located below said separator, and means for delivering the unground material from the separator to said second mill -and for returning the ground material from the latter to the separator to commingle therein with the product from the first named mill.

Signed at Walden in the county of Orange and State of New York this 5th day of May A. D. 1928.

WILLIAM J.'A. LONDON. 

